1. Field of the Invention
The present invention relates to the use of communications networks and, in particular, to the use of integrated services digital networks (ISDN).
2. Description of the Related Art
High-bandwidth communications networks such as ISDN are commonly used to communicate with specified end points or nodes of the network. ISDN lines and services are typically provided by ISDN providers, such as telephone companies. For example, a first user may desire to establish a data conference with at least a second user. In general, a data conference, sometimes also referred to as a video conference, is a conference in which the participants in the conference share audio, video, and other types of data on their respective local terminals. High-bandwidth communications may be required or desirable for such data conferences, so that audio, video, and other forms of data may be distributed to participants in the conference in real time.
A user having access to a high-bandwidth communications channel such as an ISDN line will often use the ISDN line for various communications purposes. For example, an ISDN connection may be made to the user's Internet service provider (ISP) to check email, browse sites on the world wide web (WWW), and the like. Such Internet-compatible communications may be made using H.323-compliant communications protocols and the transmission control protocol/Internet protocol (TCP/IP), a packet switching control protocol used for networks such as public networks (e.g., the Internet) and private networks (e.g. Intranets). A point-to-point data conference may also be established between two users over the Internet via the users' respective ISPs, using such H.323-compliant communications. Each user may have an ISDN connection to its respective ISP, which then establish a high-bandwidth connection with each other over the Internet.
Alternatively, instead of communicating through the Internet, a point-to-point data conference may be established directly through ISDN using H.320-compliant communications protocols. Such a direct use of ISDN does not involve the Internet or the users' ISPs, but is routed and switched in a manner similar to a standard POTS (plain old telephone system) telephone call, albeit with higher bandwidth. In addition to H.320 and H.323 connections, other International Telecommunication Union (ITU) Series H Recommendations protocols may be used for line transmission of non-telephone signals as well.
ISDN communication can be used for a variety of types of data transfer and bandwidth requirements. In an ISDN connection between two end points or users, the connection includes both a relatively low-bandwidth data channel (D channel) and typically one or two relatively high-bandwidth so-called "bearer" channels (B channels). Both B and D channels are full duplex digital communication channels. The D channel is used to switch on and control the use of B channels. To establish an ISDN connection, the D channel is used to access switch controlling to establish at least one B channel. A second B channel can be added as necessary for higher bandwidth data throughput, using the bandwidth allocation control protocol (BACP) of ISDN. For example, one B channel may be used for data and audio communications. If the users then desire to share video data as well, more bandwidth may be required, and a second B channel may be added to maintain the quality of the conference.
Unfortunately, if a first user attempts to call a second user to establish an ISDN connection with the second user, the second user may already be using all the spare capacity of his ISDN line. For example, the second user may be currently using the D channel and both B channels to engage in a conference with a third party, to access an ISP, or for another communications purpose. In this case, the first user may be unable to establish an ISDN connection with the second user with sufficient bandwidth to handle the planned use of the ISDN connection, or the first user may be unable to contact the second user at all, for example the equivalent of a busy signal may be received by the first user.